Traditionally, bipolar batteries including several cells have been designed to have separately sealed cells to contain both electrolyte and gas created during operation. A problem that has occurred is the creation of an electrolyte path between adjacent cells due to inadequate sealing properties, which in turn mainly depend on a pressure difference between adjacent cells. The pressure difference arises when a cell starts to gas before the cell next to it starts gassing. This is a normal behaviour of cells in a bipolar battery.
A solution to this problem has been suggested in U.S. Pat. No. 5,344,723 by Bronoel et al., which discloses a bipolar battery having a common gas chamber, which is created by providing an opening through the biplate (conductive support/separator). The opening is also provided with a hydrophobic barrier to prevent passage of electrolyte through the hole. Although the problem with pressure differences between the cells is solved, there is still a disadvantage with the described battery. The outer sealing around the edge of each biplate still has to be fluid-tight, which is very difficult to achieve. If the outer sealing is not fluid-tight, the electrolyte, contained in the separator between the electrodes, may form an electrolyte path from one cell to another.
Furthermore, the suggested solution is rather expensive to implement since an opening has to be made through the biplate to create the common pressure chamber. If the biplate is relatively thin, it is even harder to create an opening through the biplate because tears, stretching, or metal slivers may form.
There is a need for a battery that is easy to manufacture at affordable prices, and that are safe to handle during charge and discharge procedures.